Humidity-responsive circuit

ABSTRACT

A humidity-responsive circuit consisting of a humidity-sensing element and a power supply winding in series connected through a rectifier bridge to a relay controlling an alarm or a dehumidification control device, the relay being connected in parallel with a normally nonconducting silicon controlled rectifier. The gate electrode of the silicon controlled rectifier is energized from an adjustable network arranged to trigger the silicon controlled rectifier at a preset level of conduction of the humidity-sensing element. This shunts the relay, allowing its contacts to close, thereby energizing the alarm or dehumidification control device. Any defect causing the relay to become deenergized will thereby cause its contacts to close, providing &#39;&#39;&#39;&#39;fail-safe&#39;&#39;&#39;&#39; operation.

United States Patent [111 3,532,717

[72] Inventor Leopold Perlaky 3,419,214 12/1968 Evalds 317/148.5B

1 ig OTHER REFERENCES s fg yi 1968 Wiley, Home Appliances: Market for Solid State" ELEC- HS] Pmcmed June 1, 1971 TRONlCS, Sept. 13, 1963, pages 14- 15 copy lll 317/148.5B [73] Assignee l-Iygrodynamics, lnc. Primary Examiner-Lee T. Hix

Silver Spring, Md. Attorney-Herman L. Gordon [54] HUMIDITY-RESPONSIVE CIRCUIT ABSTRACT: A humidity-res onsive circuit consistin of a hu- P g 3 Claims, 1 Drawing Fig. midity-sensing element and a power supply winding in series [52] us Cl. 317/148 5B connected through a rectifier bridge to a relay controlling an 317 i alarm or a dehumidification control deice, the relay being [51] ML Cl i 47/32 connected in parallel with a normally nonconducting silicon [50] Field of Squid 317/148 5 controlled rectifier. The gate electrode of the silicon con- 53 5 trolled rectifier is energized from an adjustable network arranged to trigger the silicon controlled rectifier at a preset [56] References Cit d level of conduction of the humidity-sensing element. This UNITED STATES PATENTS shunts the relay, allowing contacts to close, thereby ener- 3 229 380 1 I19 6 6 w gizmg the alarm or dehumrdification control device. Any de- 3407840 10 1968 Forst 317/123PL fect causing the relay to become deenergized will thereby 317/1485}; cause its contacts to close, providing fail-safe" operation.

15 g 4 37 /9 ARM 9'? l z? [1- Dzlmwrmmu (7 J 50 38 CaurloL Dine: f 11 12 37 m4? Eli-6P0 40 J war HUMIDITY-RESPONSIVE CIRCUIT This invention relates to humidity detection and control devices, and more particularly to a humidity-responsive circuit of the type employing an electrical humidity-sensing element.

A main object of the invention is to provide a novel and improved humidity detection circuit which is simple in construction, which is reliable in operation, and which fails safe for most circuit failure conditions.

A further object of the invention is to provide an improved humidity detection and control circuit which involves relatively inexpensive components, which is compact in size, and which is relatively durable in construction.

A still further object of the invention is to provide an improved humidity detection and control circuit which fails safe when a failure occurs either in the circuit itself or in the associated power supply, so that an alarm or dehumidification control device will be energized from a standby power source when such a failure occurs, in the same manner as the circuit would normally respond to a condition of excessive humidity in the area being supervised.

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawing, wherein the single FIGURE is a schematic circuit diagram of an improved humidity detection and control circuit constructed in accordance with the present invention.

Referring to the drawing, 11 designates a conventional relay having a winding 12, a pole 13 and a stationary contact 14 engaged by pole 13 when the relay is deenergized. Designated at 15 is a device intended to be actuated responsive to the deenergization of relay 11f Said device 15 may comprise a suitable alarm device, or a dehumidification apparatus for maintaining the atmosphere of an area under supervision in a relatively dry state. Thus, pole 13 and contact 14 comprise a control switch means closing responsive to the deenergization of relay 12 for any reason.

A suitable standby power source, such as a battery 16, or any other independent power source, is connected in circuit with device 15 and the relay contacts 13, 14. Thus, the device 15 becomes energized responsive to the deenergization of relay 11.

Designated at 17 is a power supply transformer whose primary winding 18 is connected to a pair of alternating current supply conductors 19 and 20. Transformer 17 has respective secondary windings 21 and 22. One terminal of secondary 21 is connected by a wire 23 to one input terminal 24 of a conventional bridge rectifier 25 The other terminal of secondary 21 is connected by a wire 26 to one terminal 27 of a conventional bifilar-wound electrical humidity sensing element 28, located in the area being supervised. The other terminal 29 of the sensing element 28 is connected through a resistor 30 to the remaining input terminal 31 of bridge rectifier 25.

One output terminal 32 of rectifier 25 is connected by a wire 33 to one terminal of relay winding 12. The other output terminal 34 of the rectifier is connected to the sliding contact 35 of a potentiometer 36. One terminal 37 of the winding of potentiometer 36 is connected through a resistor 38 and a wire 39 to the wire 33.

One terminal of secondary 22 is connected by a wire 40 to wire 39. The other terminal of secondary 22 is connected through a resistor 41, a diode 42 and a wire 43 to the remain ing terminal of relay winding 12.

A silicon controlled rectifier 44 is connected across wires 43 and 39, and hence across relay winding 12. The remaining terminal 45 of potentiometer 36 is connected by a wire 46 to the gate electrode 47 of the silicon controlled rectifier. It will thus be seen that the voltage appearing on electrode 47 depends on the amount of rectified current flowing through potentiometer 36 and resistor 38, and this in turn depends on the input current to the rectifier. The input current to the rectifier depends upon the resistance of sensing element 28 and is therefore a function of the humidity of the area being supervised.

A resistor 48 is connected across sensing element 28, said resistor having a relatively high value, such as l megohm.

A filter capacitor 49, of the order of l00 mfd,, is connected across relay winding 12. A bypass capacitor 50 is connected across wires 46 and 39 to aid in filtering out unwanted triggering signals. Capacitor 50 has a value ofthe order of0.0l mfd.

A capacitor 51 is connected between wires 46 and 43, acting to provide more positive pull-in and dropout action of relay 11. Capacitor 51 has a value ofthe order of0.0033 mfd.

In operation, transformer 17 supplies power from secondary 22 through resistor 41 and diode 42 to relay coil 12, thereby energizing relay 11 and holding contacts 13, 14 open as long as relay coil 12 continues to be energized.

When the sensing element 28 increases its conductivity sufficiently, due to the rise in humidity beyond a specified level, it allows a sufficient current to flow in the output circuit of bridge rectifier 25 from secondary 21 to elevate gate electrode 47 to triggering potential. The point oftriggering is established in accordance with the setting of sliding contact 35.

The triggering of silicon controlled rectifier 44 establishes conductivity through said rectifier, simulating a short circuit across relay winding 12. This causes the relay 11 to drop out, closing its contacts 13, 14 and energizing the device 15.

When humidity of the area under supervision is reduced below the limit value, the sensing element 28 will not pass enough current to maintain the silicon controlled rectifier 44 in a conducting state, thereby causing relay 11 to pull in again and open its contacts 13,14, thereby deenergizing the device 15.

1t will be noted that the circuit arrangement is such that it will fail safe for most failure conditions, for example, failure of the main supply voltage to transformer primary 18, failure of one of the power supply components, shorting of the sensing element 28, failure of the relay coil itself, or shorting failure of the silicon controlled rectifier 44. Any one of the above-listed failures will cause the relay 11 to drop out, thereby energizing the device 15 in the same way as excessively high humidity conditions in the area under supervision.

It will be noted that resistor 41 acts as a current-limiting means to prevent excessive current in secondary 22 when the relay winding 12 is substantially shorted by the triggering of the silicon controlled rectifier 44.

It will be further noted that the wires 40 and 39 are connected to the cathode 52 of the silicon controlled rectifier 44, and that the diode 42 is suitably poled to provide the proper polarity of the triggering potential on gate 47.

The normal failure mode of the sensing element 28 is similar to the effect caused by high humidity, whereby the failure of said element will energize the alarm or dehumidification control device 15 by causing the load contacts 13,14 to close.

In a typical embodiment of the invention, the following values were employed for the various components of the circurt:

Resistor 48: l megohm Resistor 30: 10,000 ohms Capacitor 49: mfd., 10 v.

Potentiometer 36: 10,000 ohms Resistor 38: 1200 ohms Capacitor 51: 0.0033 mfd., 100 v.

Capacitor 50: 0.01 mfd., 100 v.

Resistor 41: 82 ohms Bridge rectifier 25, each diode: Type 1N456A Silicon controlled rectifier 44: Type 3F] 5 While a specific embodiment of an improved humidityresponsive circuit has been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

We claim:

1. A humidity-responsive circuit comprising relay means provided with load contacts biased to closed condition, a source of current, circuit means connecting said source to said relay means to energize the relay means and normally maintain said load contacts open, a normally nonconducting silicon controlled rectifier connected in shunt with said relay means and having a gating electrode, an electrical humidity-sensing element of the type whose resistance decreases with humidity, and circuit means operatively connecting said sensing element to the gating electrode of said silicon controlled rectifier and including means to develop triggering potential on said gating electrode responsive to the decrease of resistance of said sensing element to a predetermined limiting value, whereby to substantially shunt said relay means and cause closure of said load contacts, wherein said circuit means comprises impedance means and a current source connected in series with said sensing element, whereby the potential across said impedance means increases with increased conductivity of the sensing element, and means applying said potential to the gating electrode, wherein said gating electrode is connected to a point on said impedance means, wherein the sources of current comprise respective secondary windings of a common power supply transformer, wherein said circuit means includes a bridge rectifier having a pair ofinput terminals and a pair of output terminals, the sensing element being connected in series with one of said secondary windings to said input terminals, at least a portion of the impedance means being connected across said output terminals, wherein said impedance means has an adjustable contact, one of said rectifier output terminals being connected to said adjustable contact, and wherein the other rectifier output terminal is connected to a diode terminal of the silicon controlled rectifier.

2. The humidity-responsive circuit of claim 1, and wherein the other of said secondary windings is connected to said relay means in a circuit which includes a current-limiting impedance.

3. The humidity-responsive circuit of claim 1, and wherein said electrical humidity-sensing element is of the bifilarwound type. 

1. A humidity-responsive circuit comprising relay means provided with load contacts biased to closed condition, a source of current, circuit means connecting said source to said relay means to energize the relay means and normally maintain said load contacts open, a normally nonconducting silicon controlled rectifier connected in shunt with said relay means and having a gating electrode, an electrical humidity-sensing element of the type whose resistance decreases with humidity, and circuit means operatively connecting said sensing element to the gating electrode of said silicon controlled rectifier and including means to develop triggering potential on said gating electrode responsive to the decrease of resistance of said sensing element to a predetermined limiting value, whereby to substantially shunt said relay means and cause closure of said load contacts, wherein said circuit means comprises impedance means and a current source connected in series with said sensing element, whereby the potential across said impedance means increases with increased conductivity of the sensing element, and means applying said potential to the gating electrode, wherein said gating electrode is connected to a point on said impedance means, wherein the sources of current comprise respective secondary windings of a common power supply transformer, wherein said circuit means includes a bridge rectifier having a pair of input terminals and a pair of output terminals, the sensing element being connected in series with one of said secondary windings to said input terminals, at least a portion of the impedance means being connected across said output terminals, wherein said impedance means has an adjustable contact, one of said rectifier output terminals being connected to said adjustable contact, and wherein the other rectifier output terminal is connected to a diode terminal of the silicon controlled rectifier.
 2. The humidity-responsive circuit of claim 1, and wherein the other of said secondary windings is connected to said relay means in a circuit which includes a current-limiting impedance.
 3. The humidity-responsive circuit of claim 1, and wherein said electrical humidity-sensing element is of the bifilar-wound type. 